Introduction

Tremendous consumer interest in multimedia applications is driving the need for successively higher data rates in wireless networks. The IEEE 802.11n standard for high throughput Wireless Local Area Networks (WLANs) improves significantly upon the data rates experienced by end users of current WLAN systems, e.g., 802.11a, b, and g.

The soon-to-be ratified 802.11n standard specifies a high data rate multiple-input, multiple-output (MIMO) based physical layer which employs orthogonal frequency division multiplexing (OFDM) and up to four spatial streams [1]. Both high data rate and long-range coverage are achieved by employing spatial signal processing techniques such as spatial spreading and transmit beamforming [2], among others. 802.11n introduces a range of MAC-layer enhancements also, but these are beyond the scope of this chapter.

In this chapter, we give an overview of two spatial processing alternatives available to implementers of 802.11n. We examine spatial spreading and transmit beamforming schemes, as well as possible receiver structures. Comparisons in terms of performance and complexity are also given.

The chapter is organized as follows. Section 9.2 gives a brief overview of MIMO OFDM, as well as the relevant system aspects of the 802.11n physical layer (PHY). Section 9.3 describes spatial spreading. Section 9.4 describes eigenvector-based transmit beamforming and schemes for channel sounding and calibration. Section 9.5 describes receiver structure alternatives for use with the above mentioned techniques.